Efficient facemask decontamination via forced ozone convection

Abstract

The COVID-19 crisis has taken a significant toll on human life and the global economy since its start in early 2020. Healthcare professionals have been particularly vulnerable because of the unprecedented shortage of Facepiece Respirators (FPRs), which act as fundamental tools to protect the medical staff treating the coronavirus patients. In addition, many FPRs are designed to be disposable single-use devices, creating an issue related to the generation of large quantities of non-biodegradable waste. In this contribution, we describe a plasma-based decontamination technique designed to circumvent the shortages of FPRs and alleviate the environmental problems posed by waste generation. The system utilizes a Dielectric Barrier Discharge (DBD) to generate ozone and feed it through the fibers of the FPRs. The flow-through configuration is different than canonical ozone-based sterilization methods, in which the equipment is placed in a sealed ozone-containing enclosure without any flow through the mask polymer fibers. We demonstrate the rapid decontamination of surgical masks using Escherichia coli (E. coli) and Vesicular Stomatitis Virus (VSV) as model pathogens, with the flow-through configuration providing a drastic reduction in sterilization time compared to the canonical approach. We also demonstrate that there is no deterioration in mask structure or filtration efficiency resulting from sterilization. Finally, we show that this decontamination approach can be implemented using readily available tools, such as a plastic box, a glass tube, few 3D printed components, and the high-voltage power supply from a plasma globe toy. The prototype assembled for this study is portable and affordable, with effectiveness comparable to that of larger and more expensive equipment.

Figure 1

(a) Picture and (b) schematic of the DBD reactor used in the mask sterilizaton experiments.

Figure 2

Schematic of cost-effective plasma reactor build by using a commercial toy plasma-ball (top), its simplified circuit diagram (bottom left), and a picture of the system (bottom right).

Figure 3

The same system was used to characterize the chemical composition (FTIR spectrometer and IR source) and the ozone concentration (V-INR monochromator and UV lamp) after the plasma discharge.

Figure 4

(a) Lissajous Figure as a function of applied voltage, (b) coupled power and (c) FTIR measured downstream of the reacator as a functon of applied voltage. (d) FTIR measurement dowstream of the plasma reactor in plasm-on condition, right after switching off the plasa, after 2 min and after 4 min.

Figure 5

(a) Ozone concentration as a function of DBD plasma dishcarge voltage. (b) Ozone concentration as a function of time (maximum disinfection time) for 7 kV applied voltage.

Figure 6

Bacterial decontamination of surgical masks over time. (a) Fluorscent images of colony growth on agar after varying decontamination times are portrayed on the left. The image at 64 min (bottom) is overexposed as only a single colony was observed (red). In the scatter plot, each point represents the mean and S.E.M. from three technical replicates that were normalized by their respective control’s mean CFU (mean of control’s CFU was 10^3.42). Relative CFU were modelled as the sum of two exponential decays. The gray ribbon represents a 95% confidence interval calculated using a parametric bootstrap. After 64 min, we observed a 10^2.78 reduction in CFU as illustrated in the inlayed plot. (b) Optical microscope image of mask before decontamination. (c) Optical microscope image of mask after 64 min of O₃ sterlization. Major discrepancies in strand formation were not obseved.

Figure 7

(a) Voltage signal produced by the power supply of the plasma globe. (b) Lissajous Figure of the plasma globe reactor. (c) FTIR analysis of the gas composition produced by the Plasma Globe Reactor and (d) corresponding O₃ concentration produced by the plasma globe reactor as a function of time. An average of 1010 ± 5 ppm along the stability period (4 to 32 min).

Figure 8

Decontamination efficacy using different configurations. The left inset shows fluorescent images of colony growth on agar after 32 min of treatment using different configurations. Right graph shows CFU values of different configurations relative to the negative control.

Figure 9

VSV treatment results (a) VSV decontamination of surgical masks over time. Each point represents the mean and S.E.M. from three biological replicates that were normalized by the control’s mean TU (mean of control TU was 10^5.68). Relative TU were modelled as the sum of two exponential decays. The gray ribbon represents a 95% confidence interval calculated using a parametric bootstrap. After 64 min, we observed a 10^2.13 reduction in TU as illustrated in the inlayed plot. (b) Decontamination efficacy after 30 min using low-cost system on different mask types. (c) Filtration efficiency of KN95 masks as a function of treatment time. No significant changes in filtration was observed.